The present invention relates to apparatus such as portable generators for providing AC electrical energy for household and similarly sized loads and, more particularly, to a new system for supplementing household or similar AC electrical load requirements by conversion of hydrocarbon combustion energy.
The present invention is concerned with a system for supplementing AC power which is normally provided to a household or similar relatively small load by a conventional AC utility service, i.e., commercial power source, by a pre-existing power distribution network such as the wiring which normally connects the utility to household loads, such as for lighting, heating, operation of appliances, etc. The present invention is, therefore, not primarily concerned with providing auxiliary AC power in the event of failure of a utility service and is not fundamentally intended to serve as a so-called standby power source which typifies the purpose of prior art household electrical power generating systems.
Small, portable power plants including gasoline or other combustion engine drive alternators have been known for many years. These have attained a marked degree of sophistication in recent years.
For example, Papachristous U.S. Pat. No. 3,691,393 describes an engine driven generating system including an automatic starter for starting the engine in response to loss of power from a main supply, i.e., conventional utility service. Thus, the system disclosed therein is one of a standby nature to be utilized only in the event of interruption of the normal supply of electrical energy to a load. Such patent is merely representative of many teachings of the prior art of standby generator systems which are configured or adapted for providing standby electrical power in the event of failure of the normal utility power service.
On the other hand, engine-generator systems have been proposed, including automatic starting controls, for initiating operation thereof in the event of the connection of an electrical load to the engine-generator set. For example, Wichman U.S. Pat. No. 3,518,445 teaches an automatic starting control for an engine-generator which acts to start the engine automatically if a load (such as at least 40 watts) is connected to the generator.
A system such as this is intended for use with mobile units such as boats, campers and the like where it is desired to provide AC power for the lights, radios and other appliances within the mobile unit where conventional AC utility service is unavailable.
The degree of sophistication of energy supplying system for totally providing electrical power requirements of a residential or other building in lieu of that otherwise provided by an AC utility service is evidenced by Peters U.S. Pat. No. 3,678,284 wherein a most sophisticated system is described for supplying electrical and thermal energy utilization systems of a building. This system is arranged in association with electrical power from a conventional external source whereby, under certain conditions, an electrical generator of the system is adapted to be utilized to supply the entire AC power requirements of certain loads in the building. The system automatically disconnects the electrical utility supply lines whenever the system is intended to provide the AC power for such loads.
The Peters system must, for power generating purposes, disconnect the AC power lines because the system is not adapted to provide AC power at the same frequency and phase as the utility source. Another significant limitation of the Peters system is that, even though not intended to be synchronous with the utility, the generator nevertheless must be tightly controlled as to speed since the frequency of current generated does vary with variations of generator speed. This requires a large generator having high inertia and intended to operate as nearly as possible at constant speed, regardless of the amount of power to be supplied thereby. Moreover, the amount of power delivered by the power source to the generator must, at all times, be capable of accommodating the maximum electrical load required of the generator. Although disadvantageous in these several respects, the Peters system does nevertheless provide the advantage of recovering exhaust heat from the engine which operates the generator. This heat is recovered as hot air or hot water for space heating and water heating purposes.
None of these various approaches of the prior art solve certain needs long existing in our society but which in recent years have become relatively acute and are now expected to remain so. It is appropriate, in providing a background for the present invention, to examine these needs and the various problems of the prior art which are concomitant aspects of these needs.
Persons having available to them a supply of combustible hydrocarbon fuel or fuels such as oil, gasoline, natural gas, producer's gas, liquified propane (LP) gas, kerosene or alcohol have available a source of energy which can be converted to electrical energy. Electrical energy is often more useful and more readily converted to work in our electrified society than other usable forms of energy. Even more importantly, the cost of converting such hydrocarbon fuels to electrical energy can be done at lower costs per kilowatt hour in many regions than would be the case if such electrical power were purchased from a utility.
In this regard, contemporary energy extraction, distribution and delivery of electrical power from hydrocarbon fired and nuclear fission fired boilers, as through use of pressurized steam by operating steam turbines which in turn drive electrical generators, utilizing the most modern techniques, provides at best a thermodynamic efficiency of 32-39 percent. Much of the remaining energy (61-68 percent) is, of course, irretrievably lost as waste heat and wastefully warms the outdoor air above power plant smokestacks, and warms rivers and streams which are partially diverted by many electric utilities for the purpose of conveniently carrying away the waste heat. But even though utilities may generate electrical power at these relatively high efficiencies, such power further must be transmitted over long distances utilizing extremely expensive, high voltage technology wherein transmission lines often operate at potentials of hundreds of thousands of volts. During transmission further losses occur.
It would be much more efficient to convert hydrocarbon fuel, such as by the burning of natural gas or LP gas and converting such combustion to electrical energy at the locality or installation wherein electrical energy is to be utilized and to locally recover the waste heat of such combustion and conversion for a useful purpose, rather than permitting the by-product heat otherwise irretrievably to be lost as in the commercial generation of electrical power.
Home owners and other users of electrical power who have available to them such hydrocarbon fuels would long ago have been able to more economically generate electrical power if the technology had been available. Electric generating plants of the prior art, utilizing hydrocarbon fuel in internal combustion engines operating in the Otto or Diesel power cycles and coupled to electrical generators, have been capable of producing electrical power with a thermodynamic efficiency of approximately 22-28 percent. This relatively lower efficiency has militated against the adoption and use of localized power generation capabilities by home owners and the like.
Furthermore, electrical generating apparatus of the prior art typically has not been capable of providing alternating current in precise phase synchronism with the electric power supplied by utility services except where engine speed is extraordinarily tightly regulated. Yet, even in the case of operation at precisely regulated speeds, engine and generator arrangements of the prior art have not been capable of operation in such a way that best fuel efficiency can be achieved over a highly variable load demand.
The attainment of such fuel efficiency and the prolongation of the apparatus life is believed to require the operation of a prime mover over a wide range of speed. But is this were attempted utilizing engine and generator arrangements typical of the prior art, the frequency of the alternating current provided by the generator would not be in synchronism with the frequency of utility power.
It must also be recognized that, where power generating equipment is to be attached to utility service lines, it is most desirable to preclude the energy flow in the reverse direction, i.e., into the utility power distribution network. In the past, large rotating electrical machinery (such as large factory motors, elevator motors and the like), have been operated to result, under some operating conditions or circumstances such as in a dynamic braking mode, in the flow of power in the reverse direction, i.e., into the utility power distribution network with consequent disturbing variation of utility line voltage. This has caused justifiable concern on the part of the utilities and other utility customers who are connected by the utility lines network to the offending machine. This aspect of operation of certain prior art rotating machinery led to legislation and legal protection in the form of various tariffs and other utility restrictions by which customers have been restricted in the use of electrical rotating machinery wherein there is presented the possibility of flow of electrical power into the utility distribution network.